In such a device, known from GB-A-2 094 191, the tapering, rotationally symmetrical extensions of the screw and tightening bolt are of conical shape. In this case the tightening bolt can either be provided with conical extensions at its two ends, in which case both screws are then provided with conical recesses, or conversely both screws can be provided with conical extensions which engage in conical recesses of the tightening bolt, or the tightening bolt may at one end be provided with a conical extension and at the other end with a conical recess and accordingly one screw is provided with a conical recess and the other screw is provided with a conical extension. In any case, during tightening of one of the screws the tightening bolt is subjected to a tightening force which also has an axially directed component. The tightening force generates on the oppositely arranged screw a reaction force of the same magnitude, which also acts upon the tightening bolt with an axially directed force component. These two axially directed force components cause the annular surface and the end face to be pressed against each other with a specific tightening force. The strength of the tightening force depends essentially on the starting torque that is exerted upon the screw. In the case of fitting pins with smallish diameters and correspondingly small screws, the starting torque cannot be increased arbitrarily as this can lead to a breaking away of the screw threads. In the case of fitting pins with large diameters and correspondingly large screws, it has been shown that above a specific torque the tightening force no longer increases linearly with the starting torque, but can only be increased by an insignificant amount. However, the tightening force also depends on the stiffness of the connection and also the torque which is transmitted through the connection.
It is the aim of the invention, therefore, to provide a device for connecting two machine parts, in particular two tool portions of machine tools of the type mentioned at the beginning, in which, without increasing the starting torque of the screw, a substantial increase in the tightening force can be achieved by which the annular surface is pressed upon the end face.